What makes 0DTE different
With very little time left, Gamma and Theta can dominate. A contract can become sensitive near the strike and then lose value quickly if the underlying stalls or moves away.
Formula
A simple intraday expected move reference is: stock price x annualized IV x square root of remaining hours divided by calendar hours in a year. This gives a volatility range, not a trade rule.
Example
If SPY is 500, IV is 22%, and 6.5 hours remain, the expected move reference is around a few dollars. The actual move can be larger during news, rebalancing, or sudden volatility shocks.
Risk checklist
0DTE traders should check spread width, position size, stop logic, event calendar, market trend, and whether the strategy survives a fast reversal. Losses can develop quickly.